1. Field of the Invention
The present invention relates to an abnormality determination apparatus and an abnormality determination method for a valve characteristics change mechanism that determines whether or not the valve characteristics change mechanism that changes the maximum lift amount and the lift duration of an engine valve is operating normally.
2. Description of the Related Art
Japanese Patent Application Publication No. 2007-85328 (JP-A-2007-85328) discloses a valve characteristics change mechanism that changes the maximum lift amount and the lift duration of an engine valve of an internal combustion engine. In the internal combustion engine equipped with the valve characteristics change mechanism, the maximum lift amount and the lift duration of the engine valve are changed continuously in correspondence with axial displacement of a control shaft of the valve characteristics change mechanism.
The internal combustion engine including the valve characteristics change mechanism includes an actuator that converts rotational motion of a motor into linear motion of an output shaft to output the linear motion, and a rotation angle sensor that outputs a pulse signal along with rotation of the motor. Pulse signals output by the rotation angle sensor are counted to calculate a drive amount for the actuator, and the actuator is controlled such that the calculated drive amount approaches a target drive amount. Thus, the position of the control shaft of the valve characteristics change mechanism coupled to the output shaft of the actuator is controlled to change the maximum lift amount and the lift duration of the engine valve.
In order to improve the reliability of engine control by the valve characteristics change mechanism, it is necessary to ensure that the valve characteristics change mechanism is operating normally in correspondence with the drive amount of the actuator while driving the actuator. An example of a method of determining whether or not the valve characteristics change mechanism is operating normally may include providing the control shaft of the valve characteristics change mechanism with a sensor that detects the position of the control shaft and determining whether or not the position of the control shaft is changing in correspondence with changes in drive amount of the actuator. With this configuration, it is possible to determine that any abnormality is occurring in the valve characteristics change mechanism in the case where the shaft position detection sensor is not detecting displacement of the control shaft even though the actuator is being driven.
Specifically, a shaft position detection sensor is provided that outputs, as a shaft position detection value V, a signal whose magnitude changes stepwise by a predetermined amount ΔV in correspondence with displacement of the control shaft as shown in the upper part of FIG. 13. Output signals from the rotation angle sensor are counted to derive a rotation angle count value CR corresponding to the drive amount of the actuator. Then, it is determined whether or not the valve characteristics change mechanism is operating normally based on whether or not the shaft position detection value V changes by the predetermined amount ΔV or more while the rotation angle count value CR changes by a predetermined amount ΔCR. The predetermined amount ΔCR is set to a value corresponding to the amount of change in rotation angle count value CR that occurs while the shaft position detection value V changes by at least ΔV in the state where the valve characteristics change mechanism is operating normally.
With this configuration, it is estimated that the control shaft is actually displaced along with driving of the actuator in the case where the shaft position detection value V changes by ΔV while the rotation angle count value CR changes by ΔCR as indicated by the solid line in FIG. 13. On the basis of this estimation, normality determination is performed to indicate that the valve characteristics change mechanism is operating normally. In contrast, in the case where the amount of change in shaft position detection value V that occurs while the rotation angle count value CR changes by the predetermined amount ΔCR is less than ΔV, it is estimated that the control shaft is not displaced even though the actuator is driven. On the basis of this estimation, abnormality determination is performed to indicate that an abnormality is occurring in the valve characteristics change mechanism. That is, the reliability of the engine control through the valve characteristics change mechanism can be improved by determining whether or not the valve characteristics change mechanism is operating normally by monitoring changes in rotation angle count value CR corresponding to the drive amount of the actuator and shaft position detection value V output from the shaft position detection sensor as well.
In the case where abnormality determination is performed based on whether or not the shaft position detection value V changes by ΔV or more while the rotation angle count value CR changes by ΔCR as described above, however, while it is possible to determine whether or not the valve characteristics change mechanism is operating along with driving of the actuator, it may be difficult to determine whether or not the valve characteristics change mechanism is operating appropriately in correspondence with the drive amount of the motor.
For example, even if the amount of change in rotation angle count value CR relative to the amount of displacement of the control shaft is decreased as indicated by the single-dashed line in FIG. 13 because of wear of gears constituting the actuator, for example, normality determination may be performed when the shaft position detection value V changes by ΔV or more while the rotation angle count value CR changes by ΔCR.
Meanwhile, even if the rotation angle count value CR is changed halfway through as indicated by the double-dashed line in FIG. 13 because of erroneous detection by the rotation angle sensor, for example, so that the amount of change of the rotation angle count value CR does not correspond to the amount of displacement of the control shaft, normality determination may be performed when the shaft position detection value V changes by ΔV or more while the rotation angle count value CR changes by ΔCR.
The present invention has been made in view of the foregoing circumstances, and therefore aims to provide an abnormality determination apparatus and an abnormality determination method for a valve characteristics change mechanism that can determine not only whether or not the valve characteristics change mechanism is operating as an actuator is driven but also whether or not the valve characteristics change mechanism is operating appropriately in correspondence with the drive amount of the actuator, using a shaft position detection sensor whose output signal changes stepwise along with displacement of a control shaft.